Optical device for measuring position

ABSTRACT

An optical position measuring device that includes a measuring graduation and a scanning unit, which moves relative to the measuring graduation along a measuring direction. The scanning unit includes a light source, a transmitting graduation with a graduation period P AT , on which a periodic strip pattern with a strip pattern period P SM  results in case of a relative movement between the scanning unit and the measuring graduation. A detector arrangement arranged at a distance D DET  from the scanning graduation with a plurality of blocks of individual detector elements, wherein the plurality of blocks are arranged periodically with a detector period P DET  in the measuring direction. The transmitting graduation is at the distance u from the measuring graduation, the scanning graduation is at a distance v from the measuring graduation, and the detector period P DET  has been selected in accordance with the equation 
     
       
           P   DET   =m* 1 *P   v ,  
       
     
     wherein 
     
       
           m= (1 +D   DET /( u+v+D   LQ ))  
       
     
     and 
     
       
         1=1, 2, 3, . . .  
       
     
     and 
     
       
         1 /P   v =|1 /P   SM −1 /P   AT |.

Applicants claim, under 35 U.S.C. §120, the benefit of priority of thefiling date of Apr. 15, 2000 of a Patent Cooperation Treaty patentapplication, copy attached, Serial Number PCT/EP00/03441, filed on theaforementioned date, the entire contents of which are incorporatedherein by reference.

Applicants claim, under 35 U.S.C. §119, the benefit of priority of thefiling date of Apr. 22, 1999 of a German patent application, copyattached, Serial Number 199 18 101.2, filed on the aforementioned date,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical position measuring device,in particular a so-called four-grating measuring system.

2. Description of the Related Art

As a rule, such position measuring devices include a light source, atransmitting graduation arranged in front thereof, a measuringgraduation, a scanning graduation, as well as a detector arrangementwith a periodic structure of individual detector elements, whichconstitutes a fourth graduation. Here, the light source, thetransmitting graduation, the scanning graduation, as well as thedetector arrangement are as a rule arranged in a scanning unit, which ismovable in a defined measuring direction with respect to the measuringgraduation. It is possible here to lay out such systems in the form oftransmitted light systems, as well as incident light systems; it is alsopossible to create rotatory arrangements as well as linear arrangements.A corresponding measuring device is disclosed in WO 97/16704, forexample. WO 97/16704 corresponds to U.S. Pat. No. 5,886,352, the entirecontents of each of which are incorporated herein by reference. Thisdocument does not contain any further information regarding thedimensioning of the detector device.

Different variations of multi-grating transducers are also known from apublication by R. M. Pettigrew under the title “Analysis of GratingImaging and its Application to Displacement Metrology” in SPIE, vol.136, 1st European Congress on Optics Applied to Metrology (1977), pp.325 to 332. The imaging conditions in connection with multi-gratingtransducers, wherein a divergent illumination is provided, are alsodiscussed on page 328 of this publication. In this connection, divergentillumination should be understood to be one where no optical collimatordevice is arranged downstream of the light source used, i.e. the lightbeams emitted by the light source do not impinge exactly parallel on thefirst graduation in the beam path. Here, the discussion of the imagingconditions leads to the result that the enlargement factor in the beampath is determined by an arrangement, wherein the enlargement factor isdetermined from a centered elongation, starting in the measurementgraduation plane. The enlargement factor is an important parameter in asystem with divergent illumination, in that the optimal geometricdimensioning of the detector arrangement, or of the detector elements,is a deciding function of knowing the enlargement factor in the beampath.

However, in actual applications it has been shown that a beam path modelas proposed in the mentioned publication leads to a four-grating systemwhich has a poor degree of modulation of the generated scanning signals.

SUMMARY AND OBJECTS OF THE INVENTION

It is therefore an object of the present invention to disclose anoptical position measuring device on the basis of a four-gratingmeasuring system, wherein the problems discussed above are reduced asmuch as possible. In particular, a design of the detector arrangement insuch a position measuring device, which is optimized in regard to therespective system prerequisites, is to be disclosed, which assures asufficient degree of modulation of the position-dependent scanningsignals.

This object is attained by an optical position measuring device thatincludes a measuring graduation and a scanning unit, which movesrelative to the measuring graduation along a measuring direction. Thescanning unit includes a light source, a transmitting graduationarranged distant from the light source at a distance D_(LQ) and ascanning graduation with a graduation period P_(AT), on which a periodicstrip pattern with a strip pattern period P_(SM) results in case of arelative movement between the scanning unit and the measuringgraduation. A detector arrangement arranged at a distance D_(DET) fromthe scanning graduation with a plurality of blocks of individualdetector elements, wherein the plurality of blocks are arrangedperiodically with a detector period P_(DET) in the measuring direction.The transmitting graduation is at the distance u from the measuringgraduation, the scanning graduation is at a distance v from themeasuring graduation, and the detector period P_(DET) has been selectedin accordance with the equation P_(DET)=m*1*P_(v), whereinm=(1+D_(DET)/(v+v+D_(LQ))) and 1=1, 2, 3, . . . and1/P_(v)=|1/P_(SM)=1/P_(AT)|.

The measures in accordance with the present invention now assure that itis possible in connection with any arbitrary system configurations of anoptical position measuring device based on the four-grating principlewith divergent illumination to disclose an optimized design of thedetector arrangement. A good degree of modulation of theposition-dependent scanning signals in particular is assured by this.

Furthermore, the exact knowledge of the above mentioned enlargementfactor also permits the dimensioning of the position measurement devicein accordance with the present invention, which assures a definedtolerance regarding the scanning distance. Accordingly, a deviation ofthe actual scanning distance from an ideal scanning distance is alsopossible without the signal quality being decisively negativelyaffected.

As a further advantage of the four-grating system in accordance with thepresent invention is should be mentioned, that the detector arrangementhere is not arranged directly adjoining the measuring graduation, whichis movable with respect to the former. Instead, the scanning graduation,which protects the detector arrangement from possible damage by themeasuring graduation, is arranged within the scanning unit in front ofthe detector arrangement.

The position measuring device in accordance with the present inventioncan of course be realized as an incident light, as well as a transmittedlight system. In the same way it is possible to design linear, as wellas rotatary arrangements in accordance with the invention.

Further advantages, as well as details, of the optical positionmeasuring device in accordance with the present invention ensue from thefollowing description of several exemplary embodiments by means of theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an embodiment of a position measuringdevice in accordance with the present invention in an extendedrepresentation;

FIG. 2 is a top view of an exemplary embodiment of a suitable detectorarrangement of a position measuring device in accordance with thepresent invention;

FIGS. 3 to 6 show further schematic representations of parts of anembodiment of a position measuring device in accordance with the presentinvention, by which respectively relevant parameters of the presentinvention are explained.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

An embodiment of an optical position measuring device in accordance withthe invention is represented in an extended view of FIG. 1, by whichimportant geometric parameters will be explained in what follows. Itshould already be pointed out here that the representation in FIG. 1 isof course not to scale at all, but is simply intended to be used in aschematic form for explaining the various geometric parameters.

As already indicated above, the position measuring device in accordancewith the present invention is embodied as a so-called four-gratingmeasuring system and essentially includes a light source LQ, atransmitting graduation ST, a measuring graduation MT, a scanninggraduation AT, as well as a periodically designed detector arrangementD. The fourth graduation, or the fourth grating, of the positionmeasuring device is therefore embodied by the periodic detectorarrangement D.

As indicated in FIG. 1, the light source LQ, the transmitting graduationST, the scanning graduation AT, as well as the detector arrangement D,are arranged in a common scanning unit A, which is movable in themeasuring direction x with respect to the measuring graduation MT. Therepresentation of the scanning unit A in FIG. 1 is not completelycorrect with respect to the selected measuring direction, but was onlychosen in order to show which components are part of the scanning unitA.

It should be pointed out here that, besides the transmitted lightvariation represented in FIG. 1 for reasons of improved clarity, acorrespondingly embodied incident light variation of the positionmeasuring device of the present invention can also be produced. Theessential difference of such a variation lies in that a reflectingmeasuring graduation MT is then required, while in FIG. 1 a transmittedlight measuring graduation MT is employed. In the case of the incidentlight measuring graduation, the graduation MT and AT are furthermorepreferably arranged together on a transparent support, or substrate.

The position measuring device of the present invention can be employedfor an exact position determination in a numerically-controlled machinetool, for example. For this purpose, the scanning unit A and themeasuring graduation MT are connected with components of the formerwhich can be displaced with respect to each other. Theposition-dependent output signals are provided to a numeric machine toolcontrol for further processing.

The detector arrangement D of the position measuring device includes apredetermined total M (M=1, 2, 3, 4, . . . ) of periodically arrangedblocks B1 to BM, each with a predetermined number k (k=1, 2, 3, 4, . . .) individual detector elements; in the example shown, M has beenselected to equal 5 and k to equal 4. The detector period of the blocksB1 of detector elements will be identified by P_(DET) in the course ofthe further description. The individual k detector elements of theblocks B1 to B5 have not been drawn in the schematic representation ofFIG. 1. Reference is made to the following description of FIG. 2 inregard to the exact design of the detector arrangement D.

In accordance with FIG. 1, the predetermined distance between the lightsource LQ and the transmitting graduation ST is identified by D_(LQ). Inthe measuring direction x, the light source LQ has a length x_(LQ). Thevalue u represents the predetermined distance between the transmittinggraduation ST and the measuring graduation MT; the value v representsthe predetermined distance between the measuring graduation MT and thescanning graduation AT. The predetermined distance between the scanninggraduation AT and the detector arrangement D is represented by D_(DET).The values P_(ST), P_(MT) and P_(AT) respectively identify thegraduation periods of the transmitting graduation ST, the measuringgraduation MT and the scanning graduation AT, respectively. P_(AT) is apredetermined graduation period.

In the case of a transmitted light system represented here, it is ofcourse also possible to select the distance u between the transmittinggraduation ST and the measuring graduation MT, and the distance vbetween the measuring graduation MT and the scanning graduation AT, tobe unequal. But in an incident light system u=v applies as a rule forthe distances of the measuring graduation MT to the respective adjoininggraduations ST and AT.

The light beams emitted by the light source LQ pass through the variousgraduation ST and MT and provide a periodic strip pattern S of the strippattern period P_(SM) in the plane of the scanning graduation AT. Incase of a relative movement between the scanning unit A and themeasuring graduation MT, the strip pattern S undergoes adisplacement-dependent modulation, which in the end is detected for thedetermination of the respective relative positions of the measuringgraduation MT and the scanning graduation AT. A so-called Vernier scanof the strip pattern S is performed here with the aid of theperiodically designed scanning graduation AT; reference is made inregard to this to the representation in FIG. 3. In this case thescanning graduation AT has a graduation period P_(AT), which differsfrom the period P_(SM) of the strip pattern S, as well as from thegraduation periods P_(ST), P_(MT) of the transmitting and measuringgraduations ST, MT, respectively. Light portions from the strip patternS then pass through the adjoining transparent areas of the scanninggraduation AT. The various light portions are then transformed byoptoelectronic detector elements into electrical signal portions, orpartial scanning signals TAS0-TAS270 with defined relative phaserelations. For example, light portions of respectively 90° phase shiftscan proceed in the direction of the detector arrangement D throughadjoining transparent areas of the scanning graduation AT, as indicatedin FIG. 3. Each one of the transparent areas of the scanning graduationAT is furthermore definitely assigned to one of the individual kdetector elements in the detector arrangement D. Therefore, eachdetector element of the detector arrangement D detects one of the lightportions and in this way generates one of the partial scanning signalsTAS0 to TAS270 with a definite phase relation. The detector elements aresuitably wired in the detector arrangement D, or in the scanning unit Ain a way which will be explained in what follows by means of FIG. 2, sothat it is possible in the end to transmit scanning signals S0 to S270to a downstream-connected evaluation unit for further processing.

It has been recognized in accordance with the present invention that theperiodicity of the detector arrangement, i.e. the detector periodP_(DET) is of decisive importance in connection with the generation ofprecise, position-dependent scanning signals. The optimum detectorperiod P_(DET) can be expressed in accordance with the present inventionas a function of definite geometric parameters of the position measuringdevice by the following equation (1):

P_(DET)=m*I*P_(v)   Equ. (1)

In this case, I=1, 2, 3, . . . applies to the parameter I.

In accordance with the following equation (2), the value m, hereinaftercalled an enlargement factor, is

m=(1+D _(DET)/(u+v+D _(LQ)))   Equ. (2)

If, as indicated above, u is selected to equal v, the equation (2′)results:

m=(1+D _(DET)/(2*u+D _(LQ)))   Equ. (2′)

Let the value P_(v) entered into the equation (1) be called a Vernierperiod in what follows. Reference is again made to FIG. 3 for arepresentative interpretation of the value P_(v).

In accordance with the representation in FIG. 3, in the case where I=1,the Vernier period P_(v) describes the periodicity in the plane of thescanning graduation AT, by which a multiple reproduction of thephase-shifted partial scanning signals. TAS0 to TAS270 in the measuringdirection x is possible. In the example shown, P_(v) graphicallyrepresents by I=1 that distance in the plane of the scanning graduationAT, by which four phase-shifted partial scanning signals TAS0 to TAS270are obtained from four adjacent transparent areas. Accordingly, P_(v)=4*P_(AT) applies in the example represented.

In general, the Vernier period P_(V) in the scanning graduation AT as afunction of the strip pattern period P_(SM) results from the followingequation (3):

1/P _(V)=|1/P _(SM)−1/P _(AT)|  (Equ.(3)

If in the process k partial scanning signals are generated, which arephase-shifted by 360°/k, the Vernier period in accordance with equation(3′) results in case of an exact association of the transparent areas ofthe scanning graduation with defined detector elements:

P _(v)=((k*p)+1)*P _(SM)   Equ. (3′)

In the case of the equation (3′), the graduation period of the scanninggraduation was selected in accordance with equation (4):

P _(AT)=(1+I/(k*p)*P _(SM)   Equ. (4)

Here, p=1, 2, 3, . . . applies in equations (3) and (4); moreover I mustbe selected to be aliquot to k, in that when I is divided into k a wholenumber results.

In these equations, the parameter k states the number of the detecteddifferent phase positions; the parameter I describes the number of theVernier periods assigned to a detector period, while the parameter pspecifies the number of scanning fields, or scanning gaps, which areassigned to a detector element.

If p>1 is selected here, it is possible to arrange several scanninggaps, or transparent areas within a scanning period PAT. Here, in anadvantageous embodiment the distance d_(AS) of adjoining scanning gapsis d_(AS)=w*P_(SM), wherein w=0, 1, 2, . . . p−1. A design of this typerespectively permits the assignment of several equiphase scanning gapsto one detector element.

FIG. 6 shows a schematic view from above on a portion of the scanningplane, as well as the detector plane, of such an exemplary embodiment.Here, two scanning gaps AS are provided per detector element D. Acorresponding quantitative exemplary embodiment will yet be explained inwhat follows in the course of the description.

For the derivation of the equation (2), i.e. the exact determination ofthe enlargement factor m, the present invention presupposes that thecenter of the central extension, which is the basis for the derivation,lies in the plane of the light source LQ. In contrast thereto, the abovecited publication by R. M. Pettigrew suggested to start from a centerlocated in the plane of the measuring graduation MT. However, thisassumption provided detector periods P_(DET) for the position measuringdevice, which would be too large for actual use. In turn, a degree ofmodulation of the scanning signals would result from this which would betoo low, in particular in case of large scanning fields.

However, if the detector period P_(DET) is selected in accordance withthe above equations, it is possible to scan even large scanning fieldsat a high degree of modulation of the output signals. Large scanningfields in turn offer a clearly increased insensitivity to possiblesoiling.

An advantageous embodiment of a suitable detector arrangement D is shownin FIG. 2 in a top view on the detector plane. The embodiment of thedetector arrangement D represented is used for generating four outputsignals S0, S90, S180 and S270, which are modulated as a function of thedisplacement and which are respectively phase-shifted by 90° withrespect to each other. Appropriately modified variations, which provideother phase relations between the outputs signals, can of course also beproduced within the scope of the present invention.

A total of M=5 blocks B1 to B5, each with several individual detectorelements D1 to D20, are periodically arranged in the measuring directionx in the example of FIG. 2. In this exemplary embodiment, respectivelyk=4 individual detector elements D1 to D20, which are all identicallydesigned, are provided per block B1 to B5. The example includes a totaln=20 separate detector elements D1 to D20. The detector elements D1 toD20 are each arranged at a distance d_(ED) from each other, wherein thedistance d_(ED) between adjoining detector elements D1 to D20 has beenselected to be identical over the entire detector arrangement D. Eachdetector element D1 to D20 has a narrow rectangular shape, wherein thelongitudinal rectangular axis is oriented perpendicularly in thedetector plane with respect to the measuring direction x, i.e. in they-direction shown. A partial scanning system TAS0 to TAS270 of a definedphase position is generated per detector element in the course ofscanning the periodic strip pattern S.

In accordance with the present invention, the detection period P_(DET)was selected in accordance with the previously discussed equations (1)and (2) and accordingly shows the length of a block B1 to B5 with fourdetector elements D1 to D20, as shown in FIG. 2. As a result, in thecase of the arrangement shown of M=5 blocks B1 to B5, the length L_(DET)of the detector arrangement D is L_(DET)=M*P_(DET)=5*P_(DET)−d_(ed).

As can also be seen in FIG. 2, in the embodiment represented, each kth,i.e. each fourth detector element D1 to D20, is electrically connected,i.e. the first detector element D1 from the left is connected with thefifth detector element D5 from the left, with the ninth, with thethirteenth, as well as with the seventeenth detector element D9, D13,D17. The other detector elements are connected with each otheranalogously to this. Thus, a total of k=4 groups of detector elements D1to D20, respectively connected in pairs, exists which, in the case ofthe arrangement shown, provide output signals S0, S90, S180, S270, eachphase-shifted by 90°. The output signals S0, S90, S180, S270 can bepicked up at the indicated contact pads of the detector arrangement D.Accordingly, each group of detector elements wired in this way providesoutput signals with a defined phase relation, wherein the phasepositions of the k=4 different groups each differ by 90° in thisembodiment variation.

It is possible in an alternative embodiment to select k=3, from which aphase shift of 120° between the output signals would result. Inprinciple, a phase shift of 360°/k between the output signals of the kdifferent groups of wired together detector elements therefore resultsas a function of the parameter k.

In the general case, respectively k individual detector elements arearranged per block at equidistant spacings d_(ED). The distance betweenthe center positions of adjacent detector elements isx_(ED)=d_(ED)+b_(ED). In accordance with FIG. 2, the distances, or thewidths, of the individual detector elements are designated as d_(ED), orb_(ED).

The distances between the adjacent detector elements of a group, i.e.the distances between the first and the fifth detector elements D1, D5,between the fifth and the ninth detector elements D5, D9, etc., each area whole number multiple of the detector period P_(DET). In the examplerepresented in FIG. 2, this distance is respectively a single detectorperiod P_(DET).

The width b_(ED) of a single detector element D1 to D20, i.e. the widthof a rectangular detector element D1 to D20 in the measuring directionx, also is a further important parameter of the advantageous design ofthe detector arrangement D. Of particular importance here is therequirement that cross talk between adjacent phase-shifted detectorelements should be avoided as much as possible. This means in the endthat the defined assignment of the phase position of a signal portionfrom a transparent area of the scanning graduation to a defined detectorelement is always assured.

In the case of k=4 detector elements per block B1 to B5, and a detectorperiod P_(DET), the normal width b_(ED) of a single detector elementwould therefore be P_(DET)/4. Although in this case each individualdetector element D1 to D20 would register a maximum signal intensity,with a width of this type selected, the above mentioned requirement forthe least possible cross talk between adjacent detector elements cannotalways be met under certain circumstances, i.e. under certain prevailinggeometric peripheral conditions.

It has now been further established within the scope of the presentinvention how to determine the optimized width b_(ED.n) of theindividual nth detector element D1 to D20 as a function of varioussystem parameters of such a position measuring device. The equation (5)shown in what follows provides a detector element width b_(ED.n) for thenth detector element, which represents a good compromise between therequirement for the least possible cross talk between adjacent detectorelements D1 to D20, and the highest possible signal intensity which isregistered by each detector element D1 to D20. Moreover, it is possibleto determine a minimum width for each individual one of the total of ndetector elements in the detector arrangement in order to make availablea sufficient light intensity, while simultaneously avoiding cross talk:

b _(DE.n)≧(tan_(.)α_(max)=tan_(.)α_(min))*D _(DET)   Equ. (5)

The following applies here:

_(.)α_(min)=[(arctan(x _(AS.N) +P_(SM)/1−xLQ/2))/(2*u+DLQ)]−arcsin(q*λ/P _(MT))   Equ. (5.1)

and

_(.)αmax=[(arctan(x _(AS.N) +P _(SM)/2+xLQ/2))(2*u+DLQ)]+arcsin(q*λ/P_(MT))   Equ. (5.2)

wherein

x_(AS.N): is the distance of the Nth scanning gap AS from the opticalaxis OA in accordance with the definition in FIG. 4,

x_(LQ): extension of the light source in the measuring direction x,

μ: the distance between the transmitting graduation and the measuringgraduation, or between the measuring graduation and the scanninggraduation,

D_(LQ): the distance between the light source and the transmittinggraduation,

λ: the wavelength of the light source used,

q: the order of diffraction at the measuring graduation which primarilycontributes to signal yield (0, 1, 2, . . . ); in actual use, the 0thand +/−1st orders of diffraction essentially contribute to the signalyield,

P_(MT): graduation period of the measuring graduation.

It should furthermore be noted that the case where u=v is described inthe equations (5), (5.1) and (5.2), i.e. an incident light system. Theseequations can of course also be modified without problems for the casewhere n≠v.

The angles _(.)α_(min) and _(.)α_(max) inserted into the equation (5)can also be interpreted graphically. Reference is made to FIG. 5 in thisconnection. The angle of the transmitting graduation ST above the normalline, to which beams are assigned which, originating at the edge of anextensive light source LQ, still pass through a common transparent areaof the scanning graduation AT and impinge on the same detector element,is described by means of _(.)α_(min) and _(.)α_(max).

In conclusion, two concrete exemplary embodiments of position measuringdevices will be shown, wherein the parameters P_(DET) and b_(ED) weredetermined in the detector arrangement on the basis of the aboveexplained consideration in accordance with the present invention. Thediscussed variations primarily differ by the respectively selected lightsource.

The following parameters are provided for the first exemplary embodimentwith an almost point-like light source:

x_(LQ) 0.1 mm D_(LQ) 0.2 mm D_(DET) 0.2 mm u = v 0.8 mm P_(MT) 20 μmP_(ST) 40 μm P_(AT) 50 μm P_(SM) 40 μm P_(V) 200 μm

For the scanning graduation, the width of the transparent areas wasselected to be 20 μm, and the width of the opaque area to be 30 μm.

The detector period P_(DET) results from these values with the aid ofthe two equations (1) and (2) as:

P_(DET)=232 μm

With the further parameters:

x_(n) 0 (detector element on the optical axis) d_(ED) 13 μm q 0 λ 860 nm

the value b_(ED.0) results for the optimum width b_(ED.n) of a singledetector element arranged directly adjacent to the optical axis by meansof the equations (5), (5.1), (5.2) as:

b_(ED.0)=45 μm.

This value represents the optimized detector width when taking q=0, aswell as +/−1st order of diffraction, into consideration in the course ofobtaining the signal. In actual use, the appearance of cross talkbecause of the participation of further orders of diffraction istolerated, because it is possible in this way to achieve the filteringof harmonic waves in the generated scanning signals. This can benegligible cross talk of the +/=2nd orders of diffraction.

In the second quantitative exemplary embodiment of the invention, anextended light source LQ is employed, i.e. the value x_(LQ) has beenselected to be clearly greater than in the previous example. Thefollowing are preselected parameters of the system:

x_(LQ) 0.35 mm D_(LQ) 0.3 mm D_(DET) 0.35 mm u = v 0.8 mm P_(MT) 20 μmP_(ST) 40 μm P_(AT) 45 μm P_(SM) 40 μm P_(V) 360 μm

Here, the scanning graduation was dimensioned in such a way that twotransparent areas, or scanning gaps, of a respective width of 20 μm wereprovided within two scanning periods, i.e. within 2*P_(AT)=90 μm. FIG. 6shows a view from above on a portion of the scanning graduation AT, aswell as an associated section of the detector plane with the detectorelements D1 to D5 of this example.

With the aid of the two equations (1) and (2), the detector periodP_(DET) results from these values as:

P_(DET)=417 μm.

With such a design of the scanning graduation, a detector element D1 toD5, again with the optimized width b_(ED.n), is assigned on the detectorarrangement to the two transparent areas AS,1, AS,2 . . . per n*P_(AT)scanning periods on the scanning graduation. For example, the detectorelement D1 is assigned on the two scanning gaps AS,1 and AS,2, etc. Toassure a good degree of modulation, the distance of the two scanninggaps AS.1 and AS,2, by means of which equiphase signals are detected, isselected to equal P_(SM).

The optimized widths b_(ED.n) of the individual n detector elements D1to D5 can again be determined as in the previous example with the aid ofthe equations (5), (5.1) and (5.2).

With the further parameters required for this,

x_(n) 0 (detector element on the optical axis) d_(ED) 13.5 μm q 0 λ 860nm

the sought after value b_(ED.0) results by means of the equations (5),(5.1) and (5.2) as

b_(ED.0)=91 μm.

As the equations (5), (5.1) and (5.2) show, the extended light sourcehas the effect that a larger Vernier period P_(v) must basically beprovided in order to dependably avoid the mentioned cross talk. Thegraduation period P_(AT) of the scanning graduation was also selected tobe correspondingly different in this exemplary embodiment.

The invention may be embodied in other forms than those specificallydisclosed herein without departing from its spirit or essentialcharacteristics. The described embodiments are to be considered in allrespects only as illustrative and not restrictive, and the scope of theinvention is commensurate with the appended claims rather than theforegoing description.

We claim:
 1. An optical position measuring device, comprising: ameasuring graduation; a scanning unit, which moves relative to saidmeasuring graduation along a measuring direction, said scanning unitcomprising: a light source; a transmitting graduation arranged distantfrom said light source at a predetermined distance D_(LQ); a scanninggraduation with a predetermined graduation period P_(AT), on which aperiodic strip pattern with a strip pattern period P_(SM) results incase of a relative movement between said scanning unit and saidmeasuring graduation; a detector arrangement arranged at a predetermineddistance D_(DET) from said scanning graduation with a plurality ofblocks of individual detector elements, wherein said plurality of blocksare arranged periodically with a detector period P_(DET) in saidmeasuring direction; and wherein said transmitting graduation is at apredetermined distance u from said measuring graduation, said scanninggraduation is at a predetermined distance v from said measuringgraduation, and said detector period P_(DET) has been selected inaccordance with the equation P _(DET) =m*I*P _(v), wherein m=(1+D_(DET)/(u+v+D _(LQ))) and I=1, 2, 3, . . . and 1/P _(v)=|1/P _(SM)−1/P_(AT)|.
 2. The optical position measuring device in accordance withclaim 1, wherein in the case of a predetermined number k partialscanning signals phase-shifted by 360°/k, P_(v)=((k*p)I+1)*P _(SM),wherein k=1, 2, 3, 4, . . . P _(AT)=(1+I)(k*p)*P _(SM) and p=1, 2, 3, .. . , and I must be selected to be aliquot to k.
 3. The optical positionmeasuring device in accordance with claim 1, wherein said detectorarrangement comprises a predetermined number M blocks, each with apredetermined number k individual detector elements, and distancesx_(ED) of center positions of adjoining detector elements are selectedin accordance with x_(ED)=P_(DET)/k, wherein k=1, 2, 3, 4 . . . and M=1,2, 3, 4, . . . .
 4. The optical position measuring device in accordancewith claim 3, wherein k=4 individual detector elements are arranged perblock at such a distance from each other that adjacent detector elementsprovide partial scanning signals, which are phase-shifted by 90° withrespect to one another.
 5. The optical position measuring device inaccordance with claim 1, wherein each kth one of said individualdetector elements of said detector arrangement is connected with theother, so that a predetermined number k partial scanning signals with aphase shift of 360°/k are present at said detector arrangement, whereink=1, 2, 3, 4 . . . .
 6. The optical position measuring device inaccordance with claim 1, wherein each one of said individual detectorelements has a width of b_(ED.n)(tan α_(max)−tan α_(min))*D_(DET),wherein: α_(min)=[(arctan(x _(AS.N) +P _(SM)/2=x _(LQ)/2))/(2*μ+D_(LQ))]−arcsin(q*λ/P _(MT)) α_(max)=[(arctan(x _(AS.N) +P _(SM)/2+x_(LQ)/2))/(2*μ+D _(LQ))]+arcsin(q*λ/P _(MT)), wherein: x_(AS.N): is adistance of an Nth scanning gap AS from an optical axis, x_(LQ): anextension of said light source in said measuring direction, μ: adistance between said transmitting graduation and said measuringgraduation, or between said measuring graduation and said scanninggraduation, D_(LQ): a distance between said light source and saidtransmitting graduation, λ: a wavelength of said light source used, q:an order of diffraction at said measuring graduation which primarilycontributes to signal yield (0, 1, 2, . . . ); in actual use; the 0thand +/− 1st orders of diffraction essentially contribute to a signalyield, P_(MT): graduation period of said measuring graduation.
 7. Theoptical position measuring device in accordance with claim 1, whereinseveral transparent areas of said scanning graduation are assigned to adetector element of said detector arrangement.